SAN FRANCISCO, United States — For Twitter Inc., a tweet will soon be more than a form of communication or an ad -- it will be an invitation to buy.

The San Francisco-based microblogging company is testing a “buy” button so consumers can purchase directly from tweets posted on its service. Twitter is partnering with payments company Stripe Inc. to save a person’s credit-card information so users can make a purchase with just a couple of clicks, Nathan Hubbard, Twitter’s head of commerce, said in an interview.

The feature is the first step in a larger strategy to engage Twitter users so they spontaneously shop alongside updates from people they follow. The company is testing the service, which will help broaden its revenue sources, after facing investor pressure over slowing user growth. The buy button will also help demonstrate the influence of a tweet in directly driving sales for businesses.

Hubbard said the offering builds on consumer demand to get products as soon as individuals want them, using delivery services such as EBay Inc.’s EBay Now, Amazon.com Inc.’s Amazon Fresh and Uber Technologies Inc.’s cab-hailing application.

“We want to be a bridge between a consumer wanting something and getting it,” Hubbard said. “Conversations are happening every second on Twitter with artists and charities and consumers, and many of those conversations are leading to transactions already.”

Facebook’s Button

Rival Facebook Inc., which is also testing a buy button on its ads, has tried several commerce tools on its website with little success. The Menlo Park, California-based company used to let people exchange money with Facebook credits, which it later discontinued. It also recently said it would stop prompting members to send each other digital gift cards on birthdays.

Hubbard, the former president of Live Nation Entertainment Inc.'s Ticketmaster, who was hired last year before Twitter's November initial public offering, said the company will use the test to determine what kinds of posts are most successful in getting people to buy. Twitter is starting by setting up the buy button for celebrities, musical artists, non-profits and brands that already influence their followers with 140-character updates, such as Pharrell and Burberry Group Plc.

The plan centres around “commerce in the moment,” Chief Executive Officer Dick Costolo has said.

Twitter has been building up its e-commerce initiative after hiring Hubbard. In May, Twitter and Amazon, the largest online retailer, rolled out a joint service that lets members shop by hashtag. In July, Twitter agreed to buy San Francisco- based Cardspring Inc., which lets users redeem deals and discounts through merchants’ tweets.

Twitter has been rolling out other new endeavors to diversify its revenue and generate more profit from its 271 million users. Last month, the company said it was introducing video advertisements that will let marketers pay each time someone clicks to watch a video on the site.

By Sarah Frier; editors: Pui-Wing Tam, Reed Stevenson.